NEETS Module 4 − Introduction to Electrical Conductors, Wiring
Techniques, and Schematic Reading
3−21, 4−1, 4−11, Index
and Direct Current
||Alternating Current and Transformers
||Circuit Protection, Control, and Measurement
||Electrical Conductors, Wiring Techniques,
and Schematic Reading
||Generators and Motors
||Electronic Emission, Tubes, and Power Supplies
||Solid-State Devices and Power Supplies
||Wave-Generation and Wave-Shaping Circuits
||Wave Propagation, Transmission Lines, and
||Introduction to Number Systems and Logic Circuits
||- Introduction to Microelectronics
||Principles of Synchros, Servos, and Gyros
||Introduction to Test Equipment
||Radio-Frequency Communications Principles
||The Technician's Handbook, Master Glossary
||Test Methods and Practices
||Introduction to Digital Computers
||Introduction to Fiber Optics
|Note: Navy Electricity and Electronics Training
Series (NEETS) content is U.S. Navy property in the public domain.
Generally, except for overhead transmission lines,
wires or cables are protected by some form of covering. The covering may be some
type of insulator like rubber or plastic. Over this, additional layers of fibrous
braid or tape may be used and then covered with a finish or saturated with a protective
coating. If the wire or cable is installed where it is likely to receive rough treatment,
a metallic coat should be added.
The materials used to make up the protection for a wire or cable are grouped
into one of two categories: nonmetallic or metallic.
Q29. If a cable is installed where it receives rough treatment,
what should be added?
The category of nonmetallic protective coverings is divided into three areas.
These areas are (1) according to the material used as the covering, (2) according
to the saturant in which the covering was impregnated, and (3) according to the
external finish on the wire or cable. These three areas reflect three different
methods of protecting the wire or cable. These methods allow some wire or cable
to be classified under more than one category. Most of the time, however, the wire
or cable will be classified based upon the material used as the covering regardless
of whether or not a saturant or finish is applied.
Many types of nonmetallic materials are used to protect wires and cables. Fibrous
braid is by far the most common and will be discussed first.
Fibrous braid is used extensively as a protective covering for cables. This braid
is woven over the insulation to form a continuous covering without joints (figure
1-15). The braid is generally saturated with asphalt, paint, or varnish to give
added protection against moisture, flame, weathering, oil, or acid. Additionally,
the outside braid is often given a finish of stearin pitch and mica flakes, paint,
wax, lacquer, or varnish depending on the environment where the cable is to be used.
Figure 1-15. - Fibrous braid covering.
The most common type of fibrous braid is woven from light, standard, or heavy
cotton yarn. Cotton yarn comes in different colors, which allows color-coding of
the individual conductors. Cotton will not withstand all the possible environments
in which a cable may be laid. Other materials currently being used to make fibrous
braid are glazed cotton, seine twine or hawser cord, hemp, paper and cotton, jute,
asbestos, silk, rayon, and fibrous glass. The choice of which material to use depends
on the strength needed in the cable as well as how resistant it must be to its environment.
Fibrous tape coverings are frequently used as a part of the protective covering
of cables. The material of tape coverings is made into the tape before application
to the cable. The material in yarns for braid
covering is woven into fabric during the application to the cable. When tape
covering is used, it is wrapped helically around the cable with each turn overlapping
the previous turn.
The most common types of fibrous tape are rubber-filled cloth tape and a combination
of cotton cloth and rubber. Except for duct tape, tape covering is never used as
the outer covering on a cable. Tape coverings are used directly over the insulation
of individual conductors and for the inner covering over the assembled conductors
of a multiconductor cable. Frequently, tape coverings are used under the sheath
of a lead-sheathed cable. Duct tape, which is made of heavy canvas webbing saturated
with an asphalt compound, is often used over a lead-sheathed cable for protection
against corrosion and mechanical injury.
Q30. How many categories of nonmetallic protective coverings
Q31. What is the most common type of nonmetallic material used
to protect wires and cables?
Q32. What are the most common types of fibrous tape?
Woven covers, commonly called loom, are used when exceptional abrasion-resistant
qualities are required. These covers are composed of thick, heavy, long-fibered
cotton yarns woven around the cable in a circular loom, much like that used on a
fire hose. They are not braids, although braid covering are also woven; they are
Rubber and Synthetic Coverings
Rubber and synthetic coverings are not standardized. Different manufactures have
their own special compounds designated by individual trade names. These compounds
are different from the rubber compounds used to insulate cable. These compounds
have been perfected not for insulation qualities but for resistance to abrasion,
moisture, oil, gasoline, acids, earth solutions, and alkalies. None of these coverings
will provide protection against all types of exposure. Each covering has its own
particular limitations and qualifications.
Jute and Asphalt Coverings
Jute and asphalt coverings are commonly used as a cushion between cable insulation
and metallic armor. Frequently, they are also used as a corrosive-resistant covering
over a lead sheath or metallic armor. Jute and asphalt coverings consist of asphalt-impregnated
jute yarn heli-wrapped around the cable or of alternate layers of asphalt-impregnated
jute yarn. These coverings serve as a weatherproofing.
Unspun Felted Cotton
Unspun felted cotton is commonly used only in special classes of service. It
is made as a solid felted
covering for a cable.
Q33. What materials are commonly used as cushions between cable
insulation and metallic armor?
Metallic protection is of two types: sheath or armor. As with all wires and cables,
the type of protection needed will depend on the environment where the wire or cable
will be used.
Cables or wires that are continually subjected to water must be protected by
a watertight cover. This watertight cover is either a continuous metal jacket or
a rubber sheath molded around the cable.
Figure 1-16 is an example of a lead-sheathed (jacketed) cable used in power work.
This cable is a standard three-conductor type. Each conductor is insulated and then
wrapped in a layer of rubberized tape. The conductors are twisted together, and
rope or fillers are added to form a round core. Over this is wrapped a second layer
of tape called a serving. Finally, a lead sheath is molded around the cable.
Figure 1-16. - Lead-sheathed cable.
Lead-sheathed cable is one of three types currently being used: alloy lead, pure
lead, and reinforced lead. An alloy-lead sheath is much like a pure lead sheath
but is manufactured with 2-percent tin. This alloy is more resistant to gouging
and abrasion during and after installation. Reinforced lead sheath is used mainly
for oil-filled cables where high internal pressures can be expected. Reinforced
lead sheath consists of a double lead sheath. a thin tape of hard-drawn copper,
bronze, or other elastic metal (preferably nonmagnetic) is wrapped around the inner
sheath. This tape gives considerable additional strength and elasticity to the sheath,
but must be protected from corrosion. For this reason, a second lead sheath is applied
over the tape.
Metallic armor provides a tough protective covering for wires and cables. The
type, thickness, and kind of metal used to make the armor depend on three factors:
(1) the use of the conductors, (2) the environment where the conductors are to be used, and (3) the amount of rough treatment that is expected.
Figure 1-17 shows three examples of metallic armor cable: wire braid, steel tape,
and wire armor.
Figure 1-17. - Metallic armor cable.
Wire-BRAID ARMOR. - Wire-braid armor (view a of figure 1-17
), also known as basket-weave
armor, is used when light and flexible protection is needed. Wire braid is constructed
much like fibrous
braid. The metal is woven directly over the cable as the outer covering. The
metal used in this braid is galvanized steel, bronze, copper, or aluminum. Wire-braid
armor is mainly for shipboard use.
STEEL TAPE. - a second type of metallic armor is steel tape.
Steel tape covering (view B of figure 1-17) is wrapped around the cable and then
covered with a serving of jute. There are two types of steel tape armor. The first
is called interlocking armor. Interlocking armor is applied by wrapping the tape
around the cable so that each turn is overlapped by the next and is locked in place.
The second type is flat- band armor. Flat-band armor consists of two layers of steel
tape. The first layer is wrapped around the cable but is not overlapped. The second
layer is then wrapped around the cable covering the area that was not covered by
the first layer.
Wire ARMOR. - Wire armor is a layer of wound metal wire wrapped
around the cable. Wire armor is usually made of galvanized steel and can be used
over a lead sheath (see view C of figure 1-17). It can be used with the sheath as
a buried cable where moisture is a concern, or without the sheath (view D of figure
1-17) when used in buildings.
Q34. What are the two types of metallic protection?
Q35. What are the three types of lead-sheathed cables?
Q36. What are the three examples of metallic armor cable that
Coaxial cable (figure 1-18) is defined as two concentric wires, cylindrical in
shape, separated by a dielectric of some type. One wire is the center conductor
and the other is the outer conductor. These conductors are covered by a protective
jacket. The protective jacket is then covered by an outer protective armor.
Figure 1-18. - Coaxial cable.
Coaxial cables are used as transmission lines and are constructed to provide
protection against outside signal interference.
In this chapter you learned that conductors are the means for tying the various
components of an electrical or electronic system together. Many factors determine
the type of conductor to be used in a specific application. In order for you to
compare the different types and sizes of conductors, we discussed the following
Unit Size - The unit size of a conductor is the mil-foot. a
mil-foot is a circular conductor 1foot long
with a diameter of 1 mil (0.001 inch, or one-thousandth of an inch).
Conductor Sizes - The square mil and the circular mil are the
units of measure used to determine the cross-sectional area of electrical conductors.
The square mil, as it relates to a square conductor, is the cross-sectional area
of a square conductor that has a side of 1 mil. The circular mil is the cross-sectional
area of a circular conductor having a diameter of 1 mil. The circular mil area (CMA)
of a conductor is computed by squaring the diameter of the circular conductor is
mils. Thus, a wire having a diameter of 4 mils (0.004 inch) has a CMA of 42,
or 16 circular mils. If the conductor is stranded, the CMA for a strand is computed,
and the CMA for the conductor is computed by multiplying the CMA of the strand by
the number of strands. The relationship of the square mil to the circular mil is
determined by comparing the square mil area of a circular conductor having a diameter
of 1 mil (A = πr2) to the circular mil area of the same
conductor (D2). Therefore, there is 0.7854 square mil to 1 circular mil.
There are more circular mils than square mils in a given area.
Specific Resistance - The specific resistance of a substance
is the resistance in ohms offered by a unit volume (the circular-mil-foot) to the
flow of electric current. The three factors that are used to calculate the specific
resistance of a particular conductor are (1) its length, (2) its cross-sectional
area, and (3) the specific resistance of a unit volume of the substance from which
the conductor is made. The specific resistance for various sizes and lengths of
standard solid copper wire can be determined by the use of tables.
Wire Gauge - a wire gauge is used to determine the American
Standard Wire Gauge size of conductors. The measurement of a bare conductor is taken
in the slot, not in the circular area at the bottom of the slot.
Selection of Wire Size - Four factors must be considered in
selecting the proper wire size for a particular electrical circuit. These factors
are (1) conductor size, (2) the material it's made of, (3) the location of the wire
in the circuit, and (4) the type of insulation used. Some of the types of insulation used in a high-temperature environment are FEP, extruded polytetrafluoroethylene,
and silicone rubber. The ambient (surrounding) temperature of a conductor is an
important part of total conductor heating.
Copper-versus-Aluminum Conductors - The two most common metals used for electrical conductors are copper and aluminum. Some advantages of copper
over aluminum as a conductor are that copper has higher conductivity, is more ductile,
has a higher tensile strength, and can be easily soldered. Two advantages of aluminum
wire for carrying electricity over long distances are its lightness and it reduces
corona (the discharge of electricity from a wire at high potential).
Temperature Coefficient of Resistance - The temperature coefficient
of resistance is the amount of increase in the resistance of a 1-ohm sample of a
conductor per degree of temperature rise above 0º C. The resistance of copper and
other pure metals increases with an increase in temperature.
Conductor Insulation - Insulators have a resistance that is
so great that, for all practical purposes, they are nonconductors. Two fundamental
properties of insulating materials are (1) insulation resistance and (2) the resistance
to current leakage through the insulation. Dielectric strength is the ability of
the insulation material to withstand potential difference. The dielectric strength
of an insulator is determined by raising the voltage on a test sample until it breaks
Insulating Materials - Some common insulating materials have
properties and safety precautions that should be remembered. These are:
· The purpose of coating a copper conductor with tin when rubber
insulation is used is to prevent the insulation from deteriorating due to chemical
· When extruded polytetrafluoroethylene insulation is heated, caution
should be observed not to breathe the vapors.
· The most commonly used insulating materials for extremely high-voltage
conductors are varnished cambric and oil-impregnated paper.
· Magnet wire is the common name for enamel-insulated wire used in
meters, relays, small transformers, motor windings, and so forth.
· The Navy is getting away from using asbestos insulation because
asbestos fibers can cause lung disease and/or cancer.
· Asbestos insulation becomes a conductor when it gets wet.
Conductor Protection - There are several types of conductor
protection in use. The type commonly used aboard Navy ships is wire-braid armor.
Answers to Questions Q1. Through Q36.
A1. To allow comparisons between conductors of different sizes and
A2. 375 mils (move the decimal three places to the right).
A3. a circular conductor with a diameter of 1 mil and a length of
A4. The cross-sectional area of a square conductor with a side of
A5. The cross-sectional area of a circular conductor with a diameter
of 1 mil.
A6. Circular mil area (CMA) = D2 (in mils) x number
of strands0.0004 inch = 4 mils (CMA) = 42 x 19 (strands)(CMA) =
16 x 19 = 304 mils.
A7. The resistance of a unit volume of a substance.
A8. Length, cross-sectional area, and specific resistance of a unit
volume of the substance from which the conductor is made.
A9. 1,000 ft = 10.4 ohms1,500 ft = 1.5 x 0.4 = 15.6 ohms
A10. In the parallel walled slot not the circular area.
A11. Conductor size, the material it is made of the location of the
wire in a circuit, and the type of insulation used.
A12. FEP, extruded polytetrafluoroethylene, and silicone rubber.
A13. The heat surrounding the conductor is an important part of total
A14. It is light and reduces corona.
A15. It has higher conductivity, it is more ductile, it has relatively
high tensile strength, and it can be easily soldered.
A16. The amount of increase in the resistance of a 1-ohm sample of
the conductor per degree of temperature rise above 0º C
A17. It increases.
A18. Conductors have a very low resistance and insulators have a
resistance that is so great that, for all practical purposes, they are nonconductors.
A19. Insulation resistance and dielectric strength.
A20. The resistance to current leakage through the insulation.
A21. The ability of the insulation material to withstand potential
A22. By raising the voltage on a test sample until it breaks down.
A23. To prevent the rubber insulation from deteriorating due to chemical
A24. Avoid breathing the vapors when the insulation
A25. Breathing asbestos fibers can cause lung disease and/or cancer
A26. It will become a conductor.
A27. Varnished cambric and oil-impregnated paper.
A28. Magnet wire.
A29. Metallic coat.
A31. Fibrous Braid.
A32. Rubber-filled cloth tape and a combination of cotton cloth and rubber.
A33. Jute and Asphalt coverings.
A34. Sheath and armor
A35. Alloy lead, pure lead, and reinforced lead.
A36. Wire braid, steel tape, and wire armor